The Square Kilometer Array and the Cradle of

The Square Kilometer Array and the “Cradle of Life” David Wilner (Cf. A) October 27, 2006 US SKA, Cf. A 1

The Cradle of Life • A Key Science Project – image dust emission from terrestrial planet formation zone of protoplanetary disks – assess biomolecules in ISM and disks – reach qualitatively new levels of sensitivity for SETI, including possible detection of “leakage” emissions (next talk, Jill Tarter) 2

Protoplanetary Disks • T Tauri, Herbig Ae stars: several l 00’s of proto-Sun analogs, d ~ 140 pc, age 1 -10 Myr 1. 3 mm SMA Raman et al. 2006 star dust HD 169142 Dent et al. 2006 300 AU HST Grady et al. 2006 3

Planet Formation • How do terrestrial and giant planets form? • How much orbital evolution (migration)? • Is our Solar System architecture typical? • SKA uniquely accesses disk habitable zone – need cm waves: avoid high opacity – need milli-arcsec resolution: sub-AU at 140 pc – need very high sensitivity: thermal emission 4

SKA Sensitivity • flux density emitted by a disk element d. A • less than an Earth mass in sub-AU beam at 140 pc distance of nearby dark clouds 5

Grain Growth and Settling • detailed frequency dependence of dust emissivity is diagnostic of particle properties, esp. size • SKA sensitive to cm sizes, predicted to settle to disk mid-plane and seed planetesimals TW Hya 3. 5 cm dust Wilner et al NASA/JPL R. Hurt . 6

Embedded Protoplanets • protoplanet interacts tidally with disk – transfers angular mom. – opens gap – viscosity opposes r Bate et al. P. Armitage 7

Small Bodies, Large Signatures • Moon (S/2005 S 1) in Keeler Gap, Cassini (May 1, 2005) 8

Inner Disk Holes • • SEDs of some disk systems show mid-ir flux deficits suggest inner holes, radii ~ 20 to 40 AU SMA imaging, 340 GHz, 250 mas, confirms evidence for dynamical sculpting by Jovian protoplanets HD 135344 SR 21 Brown et al. , Wilner et al GM Aur 9

A Dynamic Process • orbital timescales in habitable zone are short (t ~ 1 yr) • synoptic studies track proper motions of mass concentrations • make “movies” of inner disk structure Nelson et al. 10

New Facilities, New Territory ? 10 AU 100 AU SMA today ALMA 2013? 1 AU SKA 2020? 11

Biomolecules • Universal prebioitic chemistry? • Delivery to terrestrial planet zone? • SKA uniquely accesses low excitation rotational transitions of large molecules – favorable partition function – low line confusion – high sensitivity 12

New Interstellar Molecules • GBT: 8 (secure) new species in past 2 years rich chemistry in dark clouds leading to large organic species Lovas, Hollis, Remijan et al. 13

Protoplanetary Disk Assays • molecules detected in handful of disks – – TW Hya ion-molecule reactions (HCO+) photo-processes (high CN/HCN) deuterium fractionation (DCO+) simple organics (H 2 CO) • sensitivity limited Thi et al. 14

The Cradle of Life • image terrestrial planet formation zone of disks – grain growth to pebbles – embedded protoplanets and sub-AU tidal gaps – track motions Bryden 1999 • assess biomolecules – disk abundances – locations Remijan et al. 2006 15

Philosophical Remark • Future optical/infrared searches may reveal terrestrial exoplanets that can harbor life • Radio observations into the habitable zone of protoplanetary disks will help us to understand why they are there (and why we are here) 16

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Relevance of Radio Regime • bulk of disk material is “cold” (dark!) H 2 – probed only through minor constituents • dust: continuum emission with low opacity – d. Fn = Bn(T) kn d. A, detect every dust particle; millimeter flux ~ mass, weighted by temperature – Mdisk~ 0. 001 - 0. 1 M (Beckwith et al. 1990) • gas: spectral lines of trace species (CO, HCN, . . . ) – heterodyne dn/n >106: kinematics, chemistry • no contrast problem with stellar photosphere • high resolution imaging through interferometry 18